An optical fiber sensing technology uses light waves as sensing signals and optical fibers as transmission carriers to sense and detect external signals. It superior to conventional electrical sensors in sensing modes, sensing principles, signal detection and processing, etc. Compared with conventional sensing elements, the optical fiber sensing technology has the advantages of anti-electromagnetic interference, chemical corrosion resistance, radiation resistance, no electrification, small size, light weight, easy bending, etc. In 1977, the U.S. Naval Research Laboratory (NRL) began to implement the Foss program (optical fiber sensor system) hosted by Dr. Charles M. Davis. Since then, optical fiber sensors have been introduced, and subsequent technologies such as OTDR, BOTDA and FBG have been continuously proposed. The optical fiber sensing technology is increasingly being valued and utilized, but due to its low spatial resolution, high light loss within a large transmission distance and other factors, the development of the optical fiber sensing technology toward miniaturization, long range, distribution, and high precision is seriously hindered.
When external factors such as stress, temperature, corrosion and load interfere with a concrete structure, the inside of a material may be broken or deformed. In this case, the structure will release elastic energy, i.e. acoustic emission. The acoustic emission technology is essentially sensing and collecting these acoustic emission signals by using some acoustic emission sensors, storing and discriminating these acoustic emission signals to infer possible damages and destructions in the structure, and finally determining the service condition of the concrete structure. The acoustic emission technology has the advantages of dynamism, sensitivity, integrity, etc., but there are still many defects, such as short signal transmission distance, less monitoring content, and poor anti-electromagnetic interference capability, which seriously hinder its development.
The conventional piezoelectric ceramic acoustic emission detection method has mature technology and simple operation, but still has many drawbacks. For example, the system is relatively large, cables are too many, and the anti-electromagnetic interference capability is poor. Therefore, a novel optical fiber Bragg grating type acoustic emission detection system is produced, which has high sensitivity and strong anti-electromagnetic interference capability, but this method also has serious problems that it still belongs to the current conventional point-based monitoring, which is far from meeting the current requirements of large structure, wide range of monitoring, long-distance transmission and the like. Therefore, it is necessary to develop a novel distributed sensing optical fiber type acoustic emission monitoring and detection system.